Semiconductor compounds or alloys consisting of column III and column V materials often have important electrical and/or optical properties due to the shape of its energy bands. Many of them, like InP and related compounds, GaAs and related compounds and GaN and related compounds are direct bandgap semiconductors, which have, depending upon the material, a wide emission spectrum range from far infrared to ultraviolet and are applied to different optical components such as light-emitting diodes (LEDs), laser diodes (LDs), modulators and detectors. Besides, owing to their high carrier mobilities, and high saturation velocities, they are also highly suitable for electronic components. Silicon has poor optical properties due to its indirect bandgap, but silicon is in widespread use in the whole electronics industry because of several reasons. It has rather good electrical and mechanical properties, it has a matured manufacturing technology, their wafer size is large and it is comparatively cheap. In order to take advantage of both silicon and III-V semiconductors, it is important to combine these two materials.
It is possible by conventional epitaxial techniques like MOVPE, MBE or any other related technique, to deposit III-V materials on silicon to form a seed layer. However, these seed layers will still contain a high density of dislocations due to a relatively large lattice mismatch between the deposited materials and silicon. A general method has been to use epitaxial lateral overgrowth (ELO) to filter off these dislocations but so far the openings of the mask used in this process have been on the order of micrometers. Most such processes did not effectively avoid the dislocation propagation from the seed layer into the grown layer just above the openings. As a result, the layer grown above the masked region was non-homogenous in dislocation density: it contained very large dislocation density above the openings compared to the ELO layer, which is above the mask.
One example is found in the published US patent application 2002/0066403. Here, group III-V compound semiconductor layers were grown on a substrate starting from growing areas produced using a patterned mask. Facet structures from the different growing areas were allowed to grow together and formed a relatively a thick covering layer. Here the dislocations followed the facets and were thereby somewhat reduced. However, the grown layers were relatively thick and dislocations were still found in the areas where the different facets met.
In the published International patent application WO 2006/125040, semiconductor heterostructures and methods for fabrication were presented. Masks with openings were positioned over the substrate in such an orientation that threading dislocations were decreased during growth within the openings. Narrow and relatively deep openings were to prefer, preferable directed in 45° relative to a crystallographic direction of the substrate. However, a disadvantage was that severe lattice imperfections occur when different overgrowth areas meet.